As is well known, silicon is an element that is commonly used to fabricate semiconductor wafers. In the naturally occurring forms, silicon is composed of approximately 92.2% of silicon 28 (28Si), 4.7% of silicon 29 (29Si), and 3.1% of silicon 30 (30Si). In naturally occurring semiconductors, such as silicon and germanium, thermal conductivity of the material is limited by the concentration of the isotopic species, for example, Si29, Si30. Heat distribution and extraction in a semiconductor device is limited by the thermal conductivity of the materials from which it is made. Low thermal conductivity limits the packing density of the transistors on a semiconductor wafer or the amount of power that can be generated in a device without inducing device failure.
This is because one of the limiting factors in the lifetimes of semiconductor devices used especially for high power applications is short device lifetime due to power dissipation in the device causing higher temperature resulting in degradation of the transistor. Other limiting factors include, degraded performance through decreased mobility and increased leakage and reduced reliability through electro-migration, gate oxide breakdown, latch-up and thermal runaway.
In semiconductor devices, particularly silicon devices, it is desirable that the temperature of the silicon does not exceed 200° C. or 150° C. in the case of plastic packages. A 7° C. reduction in this temperature (100° C. nominal) results in a two-fold increase in lifetimes. Thus, many manufacturers have turned to using external cooling methods, such as heatsinks to limit the temperature rise of the device. Other attempts to dissipate heat build up include, spreading the active area of the device, managing power with gated clocks, multiple threshold voltage cells, dynamic substrate bias, package solution to extract heat, and wafer thinning. Further improvements, however, in cooling technology are necessary to allow these devices to be used in various applications, such as microprocessors, digital signal processors, and integrated circuits.
Accordingly, what is needed in the art is a process and device for manufacturing a semiconductor device that does not exhibit the limitations of the prior art.